Heresy is a list of utilities for lazy and functional programming in Common Lisp. Function names are chosen and decorated so as to resemble Haskell and/or CL equivalents; but to allow full import of exported symbols into a typical namespace.

The lazy-list functions provided are for when the memory/cpu profile of lazy list evaluation, or list-based solutions requiring lazy evaluation (such as self-referencing lists, or sequences with issues running beyond some termination point) are desired. Expressive interoperation/conversion between CL sequences and lazy-lists, and control over degree of laziness are design goals. Lists can be heterogeneous (containing elements of different types), and functions named after Haskell list equivalents may be altered for lispiness..